The effect of intermittent forces on eruption of the rabbit incisor.

Rabbits were prepared so that a variable capacitance displacement transducer (VCDT) could be used to monitor the eruptive movements of a previously-amputated lower incisor, and a strain gauge transducer mounted on a relay-controlled plate was used to place precisely controlled intermittent forces opposing the erupting tooth. Forces of one or three g were applied under time conditions of one second on, nine seconds off (1:9); one second on, three seconds off (1:3); and one second on, one second off (1:1). The data indicate that with force present for 10% of the time (1:9), there was little or no effect on eruption rate. In contrast, 50% time (1:1) produced essentially the same intrusive effect as continuous force, and 25% time (1:3) gave an intermediate response. The data are consistent with the hypothesis that force duration is more important than force magnitude for the vertical equilibrium, as is the case for facio-lingual equilibrium.